It is well known that video encoders typically combine luminance and chrominance information by adding them together. The result is that the chrominance and high frequency luminance signals occupy the same portion of the frequency spectrum. Consequently, video decoders typically use some form of frequency separation filtering to separate the luminance information from the chrominance information in the composite video source information. When some luminance information is decoded as color information, cross color or false coloring conditions can occur.
Many luminance and chrominance separators are known. One type is a two dimensional (2-D) adaptive comb filter. Such separators are typically used because conventional comb filters have problems with diagonal lines and vertical color changes. Typically, with diagonal lines, after luminance and chrominance separation, the chrominance information may also include the difference between adjacent luminance values which may be interpreted by a decoder as chrominance information. The result may be false color artifacts along the edge of a line. A general discussion of an example of two-dimensional adaptive luminance and chrominance separators may be found for example in a book entitled "Video De-Mystified" authored by Keith Jack (1997), pages 294-298.
Conventional 2-D adaptive luminance and chrominance separators typically look at vertical chrominance data over multiple lines and also evaluates for horizontal chrominance information. Such filters are adaptive in that they evaluate if there is a difference between vertical and horizontal chrominance information. However, a problem arises with these separators because these separators typically choose horizontal chrominance information when there is a difference. An additional problem arises if the video image is black and white diagonal luminance information, since the luminance information can still bleed into the chrominance data.
The use of notch filtering is also known to notch out at the color burst frequency during the luminance information frequencies, such as between 0-5 MHz. However, notching out the requisite color burst frequency (hence chrominance information) also notches out luminance information at overlapping frequencies. This can result in distorted images such as a black and white striped shirt appearing gray to an observer. The notched information is typically then passed through a comb filter which then separates the luminance from chrominance information.
Consequently there exists a need for an improved false color compensation system and method for use with composite video source information. It would be desirable if such a system reduced false coloring when the video information includes data representing diagonal black and white transitions and/or black and white cross patterns.